Underground cavern for storage of hydrocarbons

ABSTRACT

A SYSTEM FOR STORING A LIQUID HYDROCARBON PRODUCT IN AN UNDERGROUND CAVERN WITH AN UPPER CAVERNS FOR HOLDING DISPLACING FLUID AND A LOWER CAVERN FOR HOLDING A LIQUID HYDROCARBON PRODUCT, DISPOSED ONE ABOVE THE OTHER AND A WELL BORE FROM THE SURFACE OF THE EARTH TO THE UPPER CAVERN EXTENDING ALSO INTO THE LOWER CAVERN WITH MEANS FOR WITHDRAWING STORED FLUID FROM THE LOWER CAVERN TO THE SURFACE OF THE EARTH AND AT THE SAME TIME ALLOWING LIQUID FROM THE UPPER CAVERN TO FLOW THROUGH THE WELL BORE TO THE LOWER CAVERN WITHOUT MIXING WITH THE LIQUID HYDROCARBON PRODUCT.

A. M. SHOOK 3,552,128

I UNDERGROUND CAVERN FOR STORAGE OF HYDROCARBONS Jan. 5,

Filed June 2, 1969 fed lel e/ Z4 Afr United States Patent 3,552,128UNDERGROUND CAVERN FOR STORAGE F HYDROCARBONS Austen M. Shook, NewOrleans, La., assignor to Texaco Inc., New York, N.Y., a corporation ofDelaware Filed June 2, 1969, Ser. No. 829,416 Int. Cl. B65g 5/00; F16k21/18; E21f 17/16 U.S. Cl. 61-.5 4 Claims ABSTRACT OF THE DISCLOSURE Asystem for storing a liquid hydrocarbon product in an underground cavernwith an upper cavern for holding displacing fluid and a lower cavern forholding a liquid hydrocarbon product, disposed one above the other and awell bore from the surface of the earth to the upper cavern extendingalso into the lower cavern with means for withdrawing stored fluid fromthe lower cavern to the surface of the earth and at the same timeallowing liquid from the upper cavern to flow through the well bore tothe lower cavern without mixing with the liquid hydrocarbon product. i

BACKGROUND OF THE INVENTION This invention relates to a system foroperating an underground fluid storage system wherein a liquidhydrocarbon product is stored in a storage cavern formed in a salt massreservoir. This invention particularly relates to a system which usesbrine as a displacing fluid and is particularly useful for underwateroperations.

In recent years, the use of underground storage caverns has been widelyadopted. These caverns are drilled, mined, dissolved or otherwise formedwithin a subterranean stratum. A common method of forming such cavernscomprises dissolving with water sufiicient salt from a salt deposit orbed to form a sizeable storage cavern.

The bores formed in the subterranean salt bed to produce the storagecaverns are in communication with the surface of the earth by means of anumber of pipes. In each bore is disposed at least one inlet pipe oroutlet pipe for introduction and removal of stored liquid hydrocarbonand for introduction and removal of a displacing or heavier fluid, whichfluid is usually saturated brine at the temperature and pressure of thecavern. Depending on the depth of the cavern and the material stored,the temperatures within the cavern may run as high as, e.g., severalhundred degrees F., and the pressure in the cavern is usually severalhundred pounds per square inch. One type storage cavern washed from asalt bed has a temperature of about 125 to 130 F. and, when storingliquid propane, the pressure runs about 400 to 500 p.s.1.

If a surface storage pit (or pits) is provided on the earths surfacewhere there is a lower temperature, for use with the displacing fluid(for example brine), there may be a problem of loss of salt at thesurface. To counteract this, the removed brine may be diluted withwater. When the cool dilute brine is pumped back into the cavern, it isunsaturated with respect to salt at the warmer cavern temperature andresaturates itself.

Thus, additional salt is dissolved from the cavern, and the cavern isthereby enlarged. Enlargement is detrimental both from a pumping and ahandling consideration,

and also because leaking may develop when all the salt in a givenlocation is dissolved.

To prevent enlargement of the cavern, additional reservoirs have beenused with consequent additional bores for inlet and outlet piping. Inthe prior art practice, a plurality of separate bores in the earth arerequired to house a hydrocarbon supply and discharge line, a dis placingfluid supply line and a gas supply line.

In this prior art practice, the hydrocarbon product and displacing fluidare in a first reservoir. The bottoms of the first and a secondreservoir are connected by a conduit, so that the displacing liquid isat least partially stored in the second reservoir where it is covered bya cushion of gas under pressure. Separate bores for hydrocarbon product,displacing fluid and gas supply at discharge lines are provided.

The prior art practice of requiring a plurality of bores increases thecost of storing a hydrocarbon product in the earth, especially inoff-shore sites where platforms must be initially constructed andequipment transported thereto.

SUMMARY OF THE INVENTION Briefly described, this invention relates to afluid storage system for storing a liquid hydrocarbon product beneaththe surface of the earth in a storage cavern wherein a separate cavernat a higher elevation than the storage cavern is provided as a reservoirfor brine at substantially formation temperature. The improvementcomprises forming the caverns one above the other, with a well boreextending downward from the earths surface into the upper cavern andfrom the upper cavern into the lower cavern. A product passageway isprovided within the well bore extending from the earths surface andterminating in the upper portion of the lower cavern. A separate gaspassageway is provided in the bore extending from the earths surface andterminating in the upper portion of the upper cavern. A brine conduit isprovided within the bore intermediate the caverns, extending from thelower portion of the upper cavern and terminating in the lower portionof the lower cavern axially and centrally of the portion of the wellbore and surrounded by the product passageway, and bypass means areprovided within the well bore adjacent the lower portion of the uppercavern whereby brine from the upper cavern may pass into the brineconduit to displace hydrocarbon product from the lower cavern upwardlythrough the product passageway.

It is an object of the present invention to provide an undergroundcavern storage system for storing a liquid hydrocarbon product, whereina single bore may be employed to service the underground reservoir.

It is another object of the present invention to provide an undergroundcavern storage system for storing a liquid hydrocarbon product, whereinthe hydrocarbon product can be withdrawn without pumping.

It is also an object of the present invention to provide an undergroundstorage system having a plurality of caverns spaced one above the other,at different levels, wherein the caverns are in communication with oneanother and with the earths surface through a single bore.

It is an additional object of the present invention to provide a bypassconstruction in the piping in an underground bore, that will permitstorage of a displacing fluid directly above the product zone of thereservoir, and at the same time, permit withdrawal of the product liquidthrough the same bore without contamination of product liquid bydisplacement liquid.

Other objects and advantages of the present invention will becomeapparent to one skilled in the art, upon consideration of theaccompanying disclosure.

BRIEF DESCRIPTION OF THE DRAWING A more complete understanding of theinvention may be had by reference to the drawing, which is an elevationin partial section through a storage system showing a preferredarrangement of apparatus in accordance with the invention. For greaterclarity, the full extent of the caverns have not been shown in thedrawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a borehole or well bore 2, is drilled from the surface of the earth 4, downthrough intervening formations such as a heterogeneous overburden 6,into an underground salt formation 8. The term salt formation is meantto include all formations containing a relatively large amount ofsoluble salt deposits, for example, water soluble salts of sodium,potassium and magnesium.

The earths surface 4 may be either ground surface, or the floor of abody of water 5 as in off-shore locations. The bore 2 is initiallyformed by drilling a top section of a large diameter in the overburden6. A surface casing 12 (for example, having an 18-inch diameter) is thenset into place and cemented at 14 to the formation. Where the overburden6 is a solid, rocklike mass which does not crumble or fragmentate, sothat it does not require lateral support, the surface casing 12 can beeliminated. The surface casing 12 is provided with a vent passage orline 16. The vent passage 16 is in communication with the atmosphere ora source of fluid at a pressure greater than atmospheric. The shaft 2,is then drilled from the bottom of the top section 10 into the saltformation 8 forming bore 18. A production casing or productionpassageway 20 of smaller diameter (for example, having a 16-inchdiameter) and extending from above the surface casing 12 to the bottomof the bore section 18, is set into place within the surface casing 12.An annulus 12a is then joined about its outer periphery to the top edgeof the surface casing 12 and about its inner periphery, to the outsideof the production casing 20 by welding or other means. The annulus 12a,acts to space the production casing 20 away from the surface casing 12and to form a seal between the production casing 20 and the surfacecasing 12.

An upper cavern 22 is formed in the salt formation 8 by methods whichare well known and which include forcing a fluid in which salt issoluble (for example, water) against the sides of the shaft 2, at thedesired elevation until a suflicient amount of salt is carried away insolution to form the desired cavity. The excess saturated salt solutionis discharged at the surface through the line 16. Openings 24 areprovided in the production casing 20 at the level of the upper cavern 22to allow fluid to pass in and out of the upper cavern 22. The productioncasing 20 is then cemented at 26 to the wall of the bore in the shaft 2below the upper cavern 22.

A lower cavern, like the upper cavern, is formed by similar well-knownmethods. The sizes of the upper cavern 22 and of the lower cavern 28 aredependent on the amount of hydrocarbon desired to be stored and theextent of the salt mass.

A bypass 30, suitably of the type described on page 3782 of the 196869Composite Catalog of Oil Field Equipment 8: Services, Gulf PublishingCompany, Houston, Tex. and described therein as a New Otis SlidingSide-Door Dual Cross-Over Assembly, is then lowered into the productioncasing 20 until it is adjacent the upper carvern 22. Upper and lowerannular packing rings 32 and 34, respectively, are set permanently intoplace against the inside surface of the production casing 20, above andbelow the bypass 30. The bypass 30 is thus anchored in place and a fluidseal is formed thereby to prevent contact between the fluid in the upperchamber 22 and the fluid in the production casing 20, outside the bypass30. The setting and sealing of annular packing rings 32 and 34 in theproduction casing 20 is a well known art. As a practical matter, thelower annular packing ring 34 is set into the production casing 20 priorto the bypass 30 being lowered therein.

An open-ended conduit 36 is lowered into the shaft 2 until the bottomend is just above the bottom of the lower cavern 28, where it is setinto place. The length of the conduit 36 is such that in this position,the top end is just above the top of the upper cavern 22. Openings 36aare provided in the conduit 36 adjacent openings 24 in the productioncasing 20 to communicate the upper cavern 22, with the bypass 30.

Exclusive passage of the fluid from the upper cavern 22 to the lowercavern 28 is provided by the openings 24, the bypass 30, the openings36a, and the conduit 36. The top end of the conduit 36 is sealed with aplug 38, preventing fluid in the conduit 36 from escaping therefrom andintermixing with fluid in the production casing 20.

The fluid in the lower cavern 28 is introduced therein or withdrawntherefrom, through an exclusive passage. This passage includes a lowerannular passage 20a, defined by the inside of the production casing 20and the outside of the conduit 36, passages 40 in the bypass 30, and theinside of the production casing 20, above the conduit 36.

The production casing 20 is sealingly connected to a pipe 42, above thesurface 4, in which is disposed a shutoff valve or other valve means 44,to control the flow of fluids therethrough.

The operation of the system for storing liquid hydrocarbon product inthe underground storage cavern described above with brine as displacingfluid, is described as follows. A fuel line containing liquidhydrocarbon under pressure is connected to the pipe 42. Valve 44 isopened. The liquid hydrocarbon is pumped from the source through theproduction casing 20, the passages 40 and the lower annular passage 20ainto the lower cavern 28. Brine in the lower cavern 28 is displaced bythe liquid hydrocarbon and flows up out of the lower cavern 28 throughthe conduit 36 and bypass 30 via the openings 36a in the conduit 36, andthrough the openings 24, into the upper cavern 22. Excess brine in theupper cavern 22 is forced up through an annular passage 20b between theproduction casing 20 and the main section 18, and annular passage 200between the production casing 20 and the surface casing 12, out throughthe line 16.

When the preestablished volume of liquid hydrocarbon product storagespace in the lower cavern 28 is reached, an operator closes the valve44, stopping the flow of liquid hydrocarbon product from entering thelower cavern 28. The volume of liquid hydrocarbon product stored can besubstantially commensurate with the volume of the lower cavern 28 or anylesser amount. When the lower cavern 28 is not substantially filled withstored liquid hydrocarbon, a residual amount of brine remains in thelower cavern 28.

To withdraw the stored liquid hydrocarbon, valve 44 is opened, and thestored liquid hydrocarbon is displaced by the brine flowing from theupper cavern 22 through the bypass 30 and the conduit 36 to the lowercavern 28. The hydrostatic pressure of the brine may be, in someinstances, suflicient to force the liquid hydrocarbon up to the surfacewithout the need for pumping. The hydrocarbon flows via the lowerannular passage 20a, the passages 40, the bypass 30 and the productioncasing 20 to the line 42 at the earths surface. The brine in the uppercavern 22 may be displaced with gas under pressure. Preferably thespacings of the caverns are such that the stored liquid hydrocarbon maybe displaced by the brine without the necessity for pumping eitherhydrocarbon or air.

In order to initiate and sustain the flow of the liquid hydrocarbonproduct to the surface without pumping hydrocarbon product or gas, thevertical distance between the upper cavern 22 and the lower cavern 28must be greater than the product of the vertical distance between thesurface and the lower cavern 28 and a fraction defined by the specificgravity of the liquid hydrocarbon product divided by the specificgravity of the brine.

Generally, the most economical displacing fluid is brine, which isreadily available. However, any fluid which is immiscible with and has asufficiently greater density than the liquid hydrocarbon to be stored,can be used as the displacing fluid.

With brine and crude oil, having respective specific gravities of 1.2(at a depth of 2000 feet) and 0.9 as components of the system, theproduct of the height of the brine in conduit 36 and the specificgravity of brine divided by the specific gravity of crude oil must begreater than the height of the crude oil in the lower annular passage20a and production casing 20, the lengths being similar units. In otherwords, when the product of the height of brine between the bottom of theupper cavern 22 and the top of the lower cavern 28 and the fractiondefined by dividing the specific gravities of brine with crude oil, isgreater than the height of crude oil between the valve 44 and the top-ofthe lower cavern 28, the crude oil may be recovered from cavern 28without pumping.

Following are specific examples of the depth, volume and arrangements ofcaverns made according to the disclosure of the present invention withvarious liquid hydrocarbons being stored in a fluid storage system usingbrine as the displacing fluid.

EXAMPLE I The bottom of the upper cavern 22 is 500 feet from thesurface. The volume of both the upper and lower cavern 22 and 28, iseach 60,000 cubic feet. The vertical distance between the bottom of theupper cavern 22 and the bottom of the lower cavern 28 is 2500 feet. Inthe lower cavern 28, 25 API crude oil is stored. The diameter of theproduction casing 20 is 24 inches, and the diameter of the surfacecasing is 36 inches. The diameter of the liner 36 is 13% inches. Theminimum pressure at valve 44 during storage operations would be 121pounds per square inch.

EXAMPLE II The bottom of the upper cavern 22 is 1000 feet from thesurface. The volume of both the upper and lower cavern 22 and 28, iseach 560,000 cubic feet. The vertical distance between the bottom of theupper cavern 22 and the bottom of the lower cavern 28 is 2000 feet. Inthe lower cavern 28, liquid propane is stored. The diameter of theproduction casing 20 is 24 inches, and the diameter of the surfacecasing is 36 inches. The diameter of the liner 36 is 13% inches. Theminimum pressure at valve 44 during storage operations would be 381pounds per square inch.

EXAMPLE III The bottom of the upper cavern 22 is 500 feet from thesurface. The volumes of both the upper and lower caverns 22 and 28 areeach 560,000 cubic feet. The vertical distance between the bottom of theupper cavern 22 and the bottom of the lower cavern 28 is 2500 feet. Inthe lower cavern 28, 38 API crude oil is stored. The diameter of theproduction casing 20 is 24 inches, and the diameter of the surfacecasing is 36 inches. The diameter of the liner 36 is 13% inches. Theminimum pressure at valve 44 during storage operations would be 211pounds per square inch.

The above examples show various density crude oils being stored in anunderground storage reservoir built according to the disclosure of thepresent invention, and withdrawn at will. Although the present inventionis particularly useful for the storage of liquid hydrocarbon product orcrude oil in offshore production areas, this invention is not limited tosuch areas or such products. Various fractions of hydrocarbons, such asliquid propane, may be stored in the manner described.

There is no requirement that the intended cavern of the presentinvention be in a salt dome. Natural or artificially produced cavernsmay be used, so long as the walls are impervious to the stored material.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

I claim:

1. In a fluid storage system for storing a liquid hydrocarbon productbeneath the surface of the earth in a storage cavern wherein a separatecavern at a higher elevation than said storage cavern is provided as areservoir for brine at substantially formation temperature, theimprovement which comprises:

(a) forming said caverns one above the other, with a well bore extendingdownward from the earths surface into said upper cavern and from saidupper cavern into said lower cavern,

(b) providing a product passageway within said well bore extending fromsaid earths surface and terminating in the upper portion of said lowercavern,

(c) providing a separate gas passageway in said bore extending from saidearths surface and terminating in the upper portion of said uppercavern,

((1) providing a brine conduit within said bore intermediate saidcaverns extending from the lower portion of said upper cavern andterminating in the lower portion of said lower cavern, axially andcentrally of said portion of said well bore and surrounded by saidproduct passageway, and

(e) providing bypass means Within said well bore adjacent the lowerportion of said upper cavern whereby brine from said upper cavern maypass into said brine conduit to displace hydrocarbon product from saidlower cavern upwardly through said product passageway.

2. A fluid storage system as described in claim 1, wherein said productpassageway is substantially concentric with said bore and said gaspassageway comprises an annular conduit surrounding said productpassageway.

3. A fluid storage system as described in claim 1,

.wherein said well bore is provided with a casing from the surface ofthe earth to the upper portion of said upper cavern, said casing formingthe outer wall of said gas conduit.

4. In a fluid storage system for storing a liquid hydrocarbon productbeneath the surface of the sea floor in a storage cavern wherein aseparate cavern at a higher elevation than said storage cavern isprovided as a reservoir for brine at substantially formationtemperature, the improvement which comprises:

(a) forming said caverns one above the other with a well bore extendingdownward from said sea floor surface into said upper cavern and fromupper cavern into said lower cavern,

(b) providing a product passageway within said well bore extending fromabove the sea surface and terminating in the upper portion of said lowercavern,

(c) providing a separate gas passageway in said bore extending fromabove said sea surface and terminating in the upper portion of saidupper cavern,

7 8 (d) providing a brine conduit within said bore inter- ReferencesCited mediate said caverns extending from the lower por- UNITED STATESPATENTS tion of said upper cavern and terminating in the lower portionof said lower cavern axially and centrally of 29349O4 5/1960 Hendnx 61'5 said portion of said well bore and surrounded by 5 3385'067 5/1968Van Eek 61'5 said product passageway, and

(e) providing bypass means within said well bore adjacent the lowerportion of said upper cavern whereby brine from said upper cavern maypass into said brine conduit to displace hydrocarbon product from 10said lower cavern upwardly through said product passageway.

JACOB SHAPIRO; Primary Examiner US. Cl. X.R.

